2-4 days: Dark Energy Poseidon (DEP)
4-10 days solo and keeping my satellite communication devices charged is critically important: 1 to 2 DEP's w/ a solar panel w/ backup power cords
8-10+ days if I need to capture important videos and photos for a friend/client: 2-3 DEPs, 1 20KmHa Anker and 2 solar panels with some redundancy in charging cords and a meter to verify charging. Nothing worse than plugging something in only to find out that something is wonky and the batteries weren't charging or discharging correctly, or at all.
I've not had the best luck with the Anker 20KmHa, particularly in colder wet weather, but they are so cheap there really isn't/wasn't a better cost/benefit alternative. I'm contemplating a non-solar source of energy since a guy can easily go 5+ days of nasty overcast weather. Probably a hand crank gizmo, but the wind and water ones look pretty cool too if you know those options are going to be available.